macOS 10.13's Disk Utility 17.0 (1626) does not recognize raw drives. Here is an example while booted from the installer, attempting to prepare a new internal drive:

However, as seen in the blue Terminal window, diskutil does recognize the drive. We'll use it to perform a quick, cursory format (e.g., diskutil eraseDisk JHFS+ NewDisk GPT disk0) to make the disk appear in Disk Utility, where further modifications can more easily be made:

Plugging in an unformatted external drive produces the usual alert, "The disk you inserted was not readable by this computer. Initialize... | Ignore | Eject", but clicking Initialize just opens Disk Utility without the disk appearing:

As shown above, clicking View > Show All Devices does not cause the raw disk to appear.